Five people who died in a murder-suicide in Pennsylvania, US have been identified as two parents and their three children, all of whom were shot to death, a local district attorney has revealed.

The parents in the incident that took place in Sinking Spring, some 60 miles east of the state capital Harrisburg, were identified as Mark and Megan Short. The three children were not officially named, the Berks County District Attorney's office said in an official Facebook post.

The district attorney said there was a note left at the scene but did not elaborate on its contents.

Investigators said a gun was found near one of the adults, but they did not specify which one.

Local media reports said the family was having financial trouble because it needed to purchase expensive medication for a baby who had to have a heart transplant.

"This is an apparent tragic domestic incident," the district attorney's office said, adding there had been domestic issues between the husband and wife.

It added a handgun was found at the scene near one of the adults and that the family's dog was also shot to death.

Local newspaper The Reading Eagle said it published a story about the family in 2014 after its newest member, a then five-month-old girl named Willow, had received a heart transplant.

It also said the family was featured in a 2015 New York Times article discussing the difficulties it was facing in obtaining and using the medication Willow needed to keep her from rejecting her transplanted heart.

The New York Times reported a Sinking Spring family of the same name was in a touch-and-go position each month on fresh supplies of medication because of stringent rules applied by pharmacies.

The little girl was expected to be stillborn, according to media reports at the time, but on May 6, 2014, Willow was born with hypoplastic left heart syndrome, a heart defect that required a risky organ transplant.

Six days later, a suitable heart donor was found.

"Someone else's child died so that my child could live," Megan Short told the Reading Eagle in 2014

Willow required daily doses of specialty pharmaceutical drugs to stop her body from rejecting the new heart, according to another profile published in the New York Times in November 2015.

"You just feel like every month, you’re hoping that they don’t mess it up,” Megan Short said in the newspaper interview.